Crystallization of HfO_2 in InAs/HfO_2 core-shell nanowires

摘要

We report the impact of deposition parameters on the structure of HfO_2 covering InAs nanowires (NWs) being potential candidates for future field-effect transistors (FETs). Molecular beam epitaxial-grown Au-free InAs NWs were covered with HfO_2 deposited by atomic-layer deposition. The impact of the film thickness as well as the deposition temperature on the occurrence and amount of crystalline HfO_2 regions was investigated by high-resolution transmission electron microscopy (TEM) and x-ray diffraction. Compared to the deposition on planar Si substrates, the formation probability of crystalline HfO_2 on InAs NWs is significantly enhanced. Here, even 3 nm thick films deposited at 250 °C are partly crystalline. Similarly, a low deposition temperature of 125 °C does not result in completely amorphous 10 nm thick HfO_2 films, they contain monoclinic as well as orthorhombic HfO_2 nanocrystals. Combining HfO_2 and Al_2O_3 into a laminate structure is capable of suppressing the formation of crystalline HfO_2 grains.